Short-term synaptic plasticity has a profound effect on the function of the neural circuit in which it is embedded. Previous work in the Nelson lab has characterized the short-term plasticity in the rat visual cortex using a quantitative (parametric) method, using trains of evoked stimuli delivered over a range of physiological frequencies. extend results previously obtained for pyramidal cells to a characterization of the short-term plasticity of inhibitory inputs to inhibitory interneurons by making whole-cell voltage-clamp recordings of nonpyramidal neurons in layers 2/3 in slices of rat neocortex. These inhibitory interneurons will be characterized and identified physiologically and morphologically. Our goals are: 1) Characterize the interneuron-interneuron synaptic plasticity of evoked IPSCs by extracellular or intracellular presynaptic stimulation; 2) Determine if the synaptic plasticity is differentially expressed depending on the interneuron subtype of the presynaptic or postsynaptic neuron; and 3) Investigate whether the interneuron-interneuron synaptic plasticity can be modified by neuro-modulatory agents such as acetylcholine. By investigating the cholinergic modulation of cortical synaptic plasticity, these results may have implications for behavioral and cognitive brain function, and the neurological disorders, such as Alzheimer's disease, which may be related cholinergic dysfunction.